How to make hollow/wooden sounds?

I should probably go with Physical modelling but how do you make those Buchla wooden sounds? Sounds a bit like in this new Microfreak at around 12:58 min till 13:23 min

Could you make such a sound with an analog synth like A4 or better digital like Op1 or DN? On DN I did something similar while exploring the engine but sounded not so nice woody/hollow like the MF. How would you even start to make such sound? Any tips welcome and much appreciated.

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A filtered square wave or triangle is often used to make hollow sounds, FM is also good for both hollow and wooden sounds, usually you will want even operator ratios and a shortish envelope on the modulator operators. Filtering and envelopes are obviously also important, for the filter you want most of the harmonics filtered out to give a dullish sound, and depending on what sort of sound you might want the filter envelope to open the filter very briefly for the strike then quickly dampen, the amplitude envelope should have a fast attack, medium decay and fairly short release, to give a struck/ping/ring type response.


Wood, like knocking on wood is best done either by FM or with a particular Comb-Filter (like in u-he Zebra). It takes a little envelope optimization for the FM to get it from bell-ish to wood-ish. Could be that with Karplus-Strong (MicroFreak) synthesis and maybe a filter this is possible too.

A dumb knocking sound can be simulated with an analogue approach like @darenager suggests. The envelopes are very important and the filter including the characteristics of the filter resonance. I would say, not every analogue synth is capable to generate a convincing wood tone.

Hollow sounds are more complicated to achieve, if they shall sound like a sound put through a tube or inside a chamber. The typical frequency structure is missing some mid-range frequencies. But from my experience a notch-filter or a EQ is not giving us exactly what we desire (at least not for me). There are some physical modelling algorithms available, which do exactly this, simulate a tube. Plaits/MicroFreak provide this and it’s called the PL.Modal, which is a modal synthesis.

TBH … and I don’t want to be negative … but to get a really good sounding hollow timbre directly from a standard analogue synth is not easy. Digital has it’s strength as well as analogue has it’s strength. IMO the spectrum of a hollow-tone is much more complex, then a standard analogue synth is prepared to deliver.

But can we do a kind of simulation of a tube or chamber by FX? I think yes.

AFAIK inside a tube there is some complex reflection and phase-difference going on between the waves. Similar goes for a chamber. Those modes weaken or kill some frequencies, which makes this tone so special. It can be compared to layer some signals, which are a little out of phase (this is sometimes a problem at the mixing desk and hollow sounds are corrected by correcting the phases and EQ-ing).

Using some layered sounds, phase shifting, delay, and reverb could work as a simulation.



Sine waves noise octave pitch and detuning.


great to see there’s already a dedicated thread as I was just about to open one… whilst everything above is very useful and informative, I’m still curious what is contributing to that character?
the Volca Kick does it right off the bat to my ears and I wouldn’t think that it’s using the method above with 3 sines… @darenager 's input is certainly helpful but applying it with my sub37 doesn’t quite get me there. I can noodle around for a bit and get close, but without being able to pinpoint what exactly got me there… granted the sound I’m after isn’t quite what the OP highlights but still somewhat in the realm… is it that ms20 filter (from the volca kick)?

Do any of you guys own NI Massive by any chance? There’s a few wooden/hollow presets there and the UI is great for tracking down how the sound is made. I don’t really use it any more but it was great for learning sound shaping/designing although Serum has pretty much over taken the throne.

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i actually do… since there about a gazillion presets, how do I get there? currently poking around in the browser… cheers

I think they’re all in alphabetical order (sorry it’s been a while since I’ve used it) so it’ll probably be somewhere down near the bottom.

thanks bud - good advice =)

d’oh. it’s called wooden tubes… but not as “knocking” as the volca kick… still great to reverse engineer. thanks again @DataStrain

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interesting exercise. the massive patch is using 2 osc with a sine-square (dafuq?) and sounds much more complex than what I’m after… however, it has the transient and “body” much more separated. almost like a fancy and short reverb rather than one piece

curious if any synth head can explain what makes the voca kick sound the way it does… would love to replicate (and learn)

An LPG (low pass gate) helps.

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interesting research trigger. now wondering how i can mimic one without having a dedicated module… i do own a few desktop filters though… thanks for this

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Alot of great woody and hollow drums and percussion for Analog Four.


Thank you :grin: @crc

But I think that Digitone or AR’s DualVCO / RimShot is better at wooden sound.

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Too late for the OP, but …

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I don t know about the theory but the M:C makes beautiful wood sounds.